皇仁書院

Over the past two decades, iodine-mediated free radical reactions have been extensively explored and employed in chemical transformations that complement traditional ionic reactions. In this review, we have updated the progress of the iodine-mediated radical reactions in organic synthesis reported between 2015 and mid-2024, and organized the reactions according to their mechanistic pathways. In general, the proposed mechanisms can be divided into four categories based on the radical initiation or its preceding steps, namely, (1) formation of a covalent X-I (X=C, N, S, Se) bond, which subsequently participates in a radical reaction; (2) formation of a noncovalent N···I bond, which assists the homolysis of the I-I bond; (3) formation of the key iodine radicals by visible-light or heat induced homolysis of I2 or by electrochemical oxidation of iodide; (4) iodine induced peroxide decomposition via single electron transfer (SET) mechanism to generate alkoxy or alkyl peroxy radicals. We hope this review will provide readers with a comprehensive update on the iodine-mediated radical reactions, thereby further inspiring more exciting advances in this emerging field.

Semiconductor nanomaterials and nanostructured interfaces have important technological applications, ranging from fuel production to electrosynthesis. Their photocatalytic activity is known to be highly heterogeneous, both in an ensemble of nanomaterials and within a single entity. Photoelectrochemical imaging techniques are potentially useful for high-resolution mapping of photo(electro)catalytic active sites; however, the nanoscale spatial resolution required for such experiments has not yet been attained. In this article, we report photoreactivity imaging of two-dimensional MoS2 photocatalysts by two modes of photoscanning electrochemical microscopy (photo-SECM): diffusion and tunneling-based modes. Diffusion-based (feedback mode) photo-SECM is used to map the electron transfer and hydrogen evolution rates on mixed-phase MoS2 nanosheets and MoS2 chemical vapor deposition (CVD)-grown triangles. An extremely high resolution of photoelectrochemical imaging (about 1-2 nm) by the tunneling mode of the photo-SECM is demonstrated.

The role of the insulating support in photocatalysis is poorly understood. Using high-resolution photo-scanning electrochemical microscopy (photo-SECM), we observed significant spatial charge separation in few-layer-thick molybdenum disulfide (MoS2) triangles attached to a SiO2 substrate. Spatially resolved surface photovoltage (SPV) measurements revealed that photogenerated holes migrate from MoS2 to the SiO2 surface and travel laterally over distances exceeding 2 μm, driven by the built-in electric field of ∼1.7 kV/cm. In thicker and less uniform flakes, the charge separation is dominated by internal driving forces within MoS2, without significant contribution from SiO2. These findings underscore the importance of insulator-semiconductor interactions for effective charge separation, suggesting a new strategy for optimizing photocatalytic systems.

We consider the split special orthogonal group $\mathrm{SO}_{N}$ defined over a $p$-adic field. We determine the structure of any $L$-packet of $\mathrm{SO}_{N}$ containing a simple supercuspidal representation (in the sense of Gross--Reeder). We also determine its endoscopic lift to a general linear group. Combined with the explicit local Langlands correspondence for simple supercuspidal representations of general linear groups, this leads us to get an explicit description of the $L$-parameter as a representation of the Weil group of $F$. Our result is new when $p=2$ and our method provides a new proof even when $p\neq2$.

The adaptive shift that favored stone tool-assisted behavior in hominins began by 3.3 million years ago. However, evidence from early archaeological sites indicates relatively short-distance stone transport dynamics similar to behaviors observed in nonhuman primates. Here we report selective raw material transport over longer distances than expected at least 2.6 million years ago. Hominins at Nyayanga, Kenya, manufactured Oldowan tools primarily from diverse nonlocal stones, pushing back the date for expanded raw material transport by over half a million years. Nonlocal cobbles were transported up to 13 kilometers for on-site reduction, resulting in assemblage patterns inconsistent with accumulations formed by repeated short-distance transport events. These findings demonstrate that early toolmakers moved stones over substantial distances, possibly in anticipation of food processing needs, representing the earliest archaeologically visible signal for the incorporation of lithic technology into landscape-scale foraging repertoires.